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题名: 黄土丘陵区小流域刺槐人工林蒸腾的时空变异研究
作者: 焦磊
学位类别: 博士
答辩日期: 2016-05
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 傅伯杰
关键词: Loess Plateau, black locust, transpiration, water balance ; 黄土高原 ; 刺槐 ; 蒸腾 ; 水平衡
其他题名: Spatio-temporal variations in stand transpiration of black locust plantations at a re-vegetation catchment in the hilly region of Loess Plateau, China
学位专业: 生态学
中文摘要:       刺槐(Robinia pseudoacacia)是黄土丘陵区广泛分布的树种,其种植的目的是控制区域严重的水土流失,恢复退化的生态系统功能。水分是半干旱黄土丘陵区植被恢复的主要限制因子,建设大范围刺槐林是否会过度消耗有限的水资源成为关注的焦点。已有研究估算了刺槐林的蒸腾速率及其影响因素,但对耗水量及其在林地水平衡中的占比仍不清楚,也就难以评估刺槐人工林对区域水循环的潜在影响。黄土丘陵区地形复杂,空间差异大;同时,这一区域历史上实施多次植被恢复工程,当前分布的刺槐林林龄并不均一,不同地形和林龄的刺槐林蒸腾之间的差异还没有明确的认识。 本研究在延安的羊圈沟小流域设置不同坡向、不同林龄的4个刺槐林长期观测样地(2013-2015年生长季)。采用树干液流技术测定刺槐液流速率(sap flux density,Fd),结合边材面积(sapwood area,As)计算单株尺度蒸腾量(Tree transpiration,Et)和林地尺度蒸腾量(stand transpiration,Ec),并同步观测太阳辐射(solar radiation,Rs)、空气温度(air temperature,Ta)、相对湿度(relative humidity,RH)、降雨量(precipitation,P)、饱和水汽压亏缺(vapor pressure deficit,VPD)等气象因子和各样地0-180 cm深度土壤含水量(soil water content, SWC) 。同时,采用自制蒸渗仪测定林地土壤蒸发量(soil evaporation,Es),采用Gash模型估算冠层截留(canopy interception,Ei)。主要研究目标是揭示地形坡向和林龄对刺槐人工林蒸腾时空动态的影响及其机理,分析林分蒸腾在整个水量平衡中的作用,深入认识刺槐人工林的生态水文过程,以期为实现黄土丘陵区可持续的植被建设和优化水资源管理提供理论依据。 主要研究结果包括以下几个方面:
1)在2013-2015年生长季(5-9月),羊圈沟4个刺槐林观测样地生长季总Ec在21.3-57.6 mm之间,占生长季降雨量的3.41-26.17%,占潜在蒸散发(potential evapotranspiration,ET0)的3.42-9.54%。在蒸散发(evapotranspiration,ET)中,3个组分的大小关系是:Es>Ec>Ei。刺槐林地Es是Ec的2倍多,通过Es损失的水分最多。与过去普遍认为刺槐林耗水量较大的观点相比,本文的研究结果表明黄土丘陵区刺槐林蒸腾量较小,这一方面可能因为研究区刺槐人工林的林分密度较小,另一方面也反映出刺槐已经对区域干旱、当地土壤水分状况建立起了生理生态的适应机制。
2)在不同时间尺度上,影响刺槐林Ec的因子有所不同。在小时尺度上,羊圈沟4个刺槐林Ec与Rs、VPD、Ta呈极显著正相关,与RH呈极显著的负相关,说明Ec受到Rs、VPD、Ta和RH的共同影响。在日尺度上,Ec对Rs和VPD的响应是非线性的,可以用饱和指数增长模型(y=ae-bx)来解释。在月尺度上,叶面积指数(LAI)是控制刺槐林月蒸腾的决定因子。因此,获取精确的LAI数据对于准确估算和预测刺槐林月蒸腾是至关重要的。
3)2个典型年龄段(12年和28年)刺槐Et和Ec差异的结果表明,28年刺槐Et和Ec都要显著地大于12年(p<0.05)。降雨后28年刺槐Fd较降雨前增加了9%,而12年刺槐只增加了5%。28年刺槐的水力导度和气孔导度都大于12年刺槐,这是导致28年刺槐的蒸腾耗水量大的原因,也说明了28年刺槐的生理活性更旺盛。
4)在羊圈沟小流域,对比了林龄相同、坡向不同(东坡和南坡)的刺槐林蒸腾的差异。结果表明,2013和2014生长季东坡刺槐林Ec大于南坡,而2015年生长季却是南坡大于东坡。在不同土壤水分条件下,两个坡向Ec的大小关系不同。当土壤相对可提取水量(relative extractable water, REW)大于0.4时,东坡蒸腾量大于南坡,而当REW小于0.4时,南坡Ec大于东坡。因此,不同坡向刺槐林蒸腾存在差异,但是年蒸腾量在坡向之间的大小关系存在年际差异,并且对土壤水分状况的响应不同。这就使得估算小流域尺度刺槐林蒸腾存在更大的不确定性。
    综上所述,地形和林分年龄的差异可以显著影响刺槐人工林蒸腾量的时空动态。地形和林分年龄在估算和模拟小流域和区域尺度植被蒸腾耗水中是不能忽视的两个关键因子。在本研究时间段内,研究区的4个刺槐人工林在既定的林分密度和立地条件下其蒸腾对林地水量平衡的影响有限,但其长期的水文效应还需要做更长时间尺度和更深入的研究。
英文摘要:     In the hilly region of Chinese Loess Plateau, black locust (Robinia pseudoacacia) was widely planted for soil conservation and afforestation purposes during the past three decades. Water shortage is regarded as one of the most limiting factor for the success of revegetation in this region. Concerns about the impact of black locust plantations on regional water source were raised due to their potential higher transpiration. Previous studies have estimated the stand transpiration (Ec) of the plantations in this region. However, the proportion of Ec in precipitation (P) and the potential influence of Ec on water cycling in the plantation are not clear. In addition, the hilly region of Loess Plateau is characterized by highly spatial heterogeneity of topography. The effect of slope aspect on black locust transpiration is poorly studied. Moreover, the age of the black locust trees across the Loess Plateau is not uniform, because afforestation is implemented over several decades. Studies on comparison of transpiration between different aged trees or stands are absent.
    In this study, four black locust plantations were selected in Yangjuangou catchment in Loess Plateau, China. Sap flux density (Fd) and environmental variables, including solar radiation (Rs), air temperature (Ta), relative humidity (RH) and soil water content (SWC), were simultaneously monitored throughout the growing seasons in 2013, 2014 and 2015. Tree transpiration (Et) was the product of Fd and sapwood area (AS), and stand transpiration (Ec) was calculated basing on the stand sap flux density (Js) and stand total sapwood area (AST). Soil evaporation (Es) was measured by weighing lysimeters. Canopy interception (Ei) was estimated using the Gash model. The main results are as follows:
1) Total Ec of the plantations during three consecutive growing seasons ranged from 21.3 to 57.6 mm in Yangjuangou catchment, accounting for 3.41-26.17% of the precipitation and for 3.42-9.54% of potential evapotranspiration (ET0). We also examined the contribution of three ET components in the black locust plantation. Es was the dominant evaporation flux and accounting for approximately 60% of ET, followed by Ec with approximately 25% of ET. Contrary to common belief than the black locust plantations used a large amount of water, we found that the plantations had rather low transpiration rate, which possible related to their long-term adaption to local soil water conditions. The results suggests that the major water loss from the black locust plantation is not transpiration in Yangjuangou catchment.
2) The factors that impacting Ec of black locust plantation were varied at different temporal scales. Hourly mean Ec was significantly positive correlated with Rs, vapor pressure deficit (VPD) and Ta, and significantly negative correlated with RH. It is obvious that these factors have a combined effect on hourly Ec. At the daily scale, we found that responses of Ec to Rs and VPD were well explained by an exponential saturation model. Whereas, the step regression showed that LAI was the dominate factor controlling Ec at monthly scale. Therefore, accurate LAI data (e.g., from monitoring and remote sensing products) is necessary to estimate accurate monthly Ec in this region.
3) Black locust plantations with two representative age classes (12 and 28 years old) were selected in the Yangjuangou catchment on the semi-arid Loess Plateau. Our results showed that tree transpiration (Et) and Ec were higher in the 28-year-old stand than in the 12-year-old stand. The stomatal conductance (gs) and hydraulic conductance of 28-year-old trees were also higher than those of 12-year-old trees, and the two parameters were thus the causes of variations in transpiration between different age classes. After rainfall, mean Fd increased by 9% in 28-year-old trees and by 5% in 12-year-old trees. This study thus suggests that stand age should be considered for estimating transpiration at the catchment and region scales in this region. These results provide ecophysiological evidences that the older black locust trees have more active physiological status than the young ones in this region. These findings also provide basic information for the management of water resources and forests on the semi-arid Loess Plateau.
4) This study also examined the differences in Ec of black locust plantations between east slope aspect and south slope aspect in Yangjuangou catchment. The results showed that total Ec between the two slope aspects was different during the three growing seasons. Total Ec on the east slope was higher than that on the south slope in 2013 and 2014, while total Ec on the east slope was less than that on the south slope in 2015. Under the stressed soil water condition when relative extractable water (REW)<0.4, Ec on south slope aspect was higher than that on east slope. Additionally, under the non-stressed soil water condition when REW>0.4, Ec on south slope aspect was lower than that on east slope. The results suggest that response of Ec of black locust plantation to soil water condition is different between east and south slope aspects. Our study provides valuable information for estimating watershed-scale vegetation water use and enriches knowledge of optimizing the terrestrial process model in this fragile region.
    In summary, variations in topography and stand age exert significant influences on spatio-temporal dynamics of Ec in black locust plantations. For estimating and modeling vegetation transpiration at watershed and regional scales, topography and stand age are two essential factors that should be seriously taken into consideration. During the study period in this study, the negative effects of the four black locust plantations on water balance have not been exhibited. However, muti-year observations should be conducted to further investigate the long-term hydrological effects of the plantations on water cycling at stand, watershed and regional scales.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/36870
Appears in Collections:城市与区域生态国家重点实验室_学位论文

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Recommended Citation:
焦磊. 黄土丘陵区小流域刺槐人工林蒸腾的时空变异研究[D]. 北京. 中国科学院研究生院. 2016.
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